diff --git a/gl/types_common.go b/gl/types_common.go
index d02acdd..e2c7b48 100644
--- a/gl/types_common.go
+++ b/gl/types_common.go
@@ -27,22 +27,22 @@ func (u Uniform) WriteAffine(a *f32.Affine) {
 // WriteMat4 writes the contents of a 4x4 matrix to a GL uniform.
 func (u Uniform) WriteMat4(p *f32.Mat4) {
 	var m [16]float32
-	m[0*3+0] = p[0][0]
-	m[0*3+1] = p[1][0]
-	m[0*3+2] = p[2][0]
-	m[0*3+3] = p[3][0]
-	m[1*3+0] = p[0][1]
-	m[1*3+1] = p[1][1]
-	m[1*3+2] = p[2][1]
-	m[1*3+3] = p[3][1]
-	m[2*3+0] = p[0][2]
-	m[2*3+1] = p[1][2]
-	m[2*3+2] = p[2][2]
-	m[2*3+3] = p[3][2]
-	m[3*3+0] = p[0][3]
-	m[3*3+1] = p[1][3]
-	m[3*3+2] = p[2][3]
-	m[3*3+3] = p[3][3]
+	m[0*4+0] = p[0][0]
+	m[0*4+1] = p[1][0]
+	m[0*4+2] = p[2][0]
+	m[0*4+3] = p[3][0]
+	m[1*4+0] = p[0][1]
+	m[1*4+1] = p[1][1]
+	m[1*4+2] = p[2][1]
+	m[1*4+3] = p[3][1]
+	m[2*4+0] = p[0][2]
+	m[2*4+1] = p[1][2]
+	m[2*4+2] = p[2][2]
+	m[2*4+3] = p[3][2]
+	m[3*4+0] = p[0][3]
+	m[3*4+1] = p[1][3]
+	m[3*4+2] = p[2][3]
+	m[3*4+3] = p[3][3]
 	UniformMatrix4fv(u, m[:])
 }